As connecting materials in such a case that flexible boards and electronic components (flip chips etc.) equipped with connection-purpose terminals are connected to wiring boards in electrically conductive manners, thermosetting resins have been widely employed. A thermosetting resin has a property that when the thermosetting resin is heated, polymerization occurs, a mesh structure of macromolecular is formed, and then, the thermosetting resin is hardened. As a consequence, under such a condition that a thermosetting resin is interposed between an electronic component and a wiring board (generally speaking, under such a condition that electronic component is mounted on wiring board where thermosetting resin has been previously coated), heat is applied from the side of the electronic component, or from the side of the wiring board, so that the thermosetting resin is hardened, and thus, the electronic component is connected to the wiring board.
As to wiring boards, there are many cases that a large number of wiring boards have been manufactured by forming resins. As a result, these resin wiring boards may absorb moisture when the resin wiring boards are stored, or are transported after the productions thereof. As previously explained, when the thermosetting resins are heated the wiring boards are also heated. As a result, there are some possibilities that the absorbed components are vaporized to be left as voids within the hardened resins. Since the voids left in the hardened resins may cause a factor for deteriorating connection reliability, conventionally, dehumidification has been carried out by which the wiring boards themselves before electronic components are mounted are heated so as to vaporize the absorbed components (refer to patent publication 1)
[Patent Publication 1] JP-A-10-223686